Critical Aspects of the Cracked Brazilian-disc test Explored by the Method of Caustics

Abstract

Some critical aspects of the cracked Brazilian-disc test are explored in the light of recently introduced analytic solutions for the stress- and displacement-fields developed in a centrally cracked cylindrical disc under uniform pressure (acting along two finite arcs of its periphery symmetric with respect to the disc's center). The study is focused to the reliable determination of the respective Stress Intensity Factors (SIFs) and also to the role of the actual boundary conditions along the disc-jaw contact arc (assuming that the disc is compressed between the curved jaws of the device suggested by the International Society for Rock Mechanics (ISRM) for the standardized implementation of the Brazilian-disc test). The crack is assumed relatively short with respect to the disc's radius. The results of the analytic approach concerning the SIFs and the length of the disc-jaw contact arc are compared to the respective ones obtained experimentally using the method of Caustics. The agreement is satisfactory at least for load levels for which the linearity assumption is not violated. Taking advantage of the insight gained additional issues related to the validity of the test as a mean to determine mode-I fracture toughness are critically discussed revealing that quite a few questions are still open although the test is standardized by ISRM almost since 20 years.